I have recently bought some MKP film capacitors to make a capacitor bank in parallel. While viewing their datasheet, it was mentioned that the soldering temperature should not be over 600 degrees Fahrenheit. Is it recommended to fix them on a soldering board or am I better off designing a PCB and fixing them?
TDK recommends more like 500F (260 C) for less than 10 seconds for their MKP polypropylene box film caps. PP melts in around there, and softens at a much lower temperature, so the exposure must be brief enough that the heat does not travel up into the body to much of a degree. For that reason I don't think you will find SMT polypropylene capacitors despite their favorable characteristics for some purposes (low dielectric absorption).
It should not be a problem for hand soldering into a PCB or deftly attaching reasonable-size wires (say AWG 20 or 22), but if you are planning to solder caps to massive bus bars you may have problems unless the leads are left long and heat sinked during soldering.